1. Field of the Invention
The present invention relates to a semiconductor device used for a capacitor microphone.
2. Description of the Related Art
A portable telephone makes heavy use of electric capacitor microphones (hereinafter referred to as ECMs). An example of such a system is disclosed in JP-A-11-88992. In this example, a fixed electrode layer is formed in an integrated semiconductor substrate and a vibrating film is attached to the fixed electrode layer through a spacer.
The structure of this example is shown in FIG. 6 in which a fixed electrode layer, an insulating film 113, a spacer 114 and a vibrating film are successively stacked on the surface of a silicon semiconductor substrate 111. The resultant laminated structure is mounted in a package 118 having a hole 116. A cloth 117 may be formed as necessary. A junction type FET element for impedance conversion, an amplifier circuit, a noise canceling circuit, etc. are integrated on the surface of the semiconductor circuit by an ordinary semiconductor process. The capacitor formed by the vibrating film 115 and fixed electrode layer changes its own capacitance when air vibration vibrates the vibrating film 115. A change in the capacitance is supplied to the FET element so that it is converted into an electric signal.
In such a configuration, in order to increase the capacitance of the capacitor so that the output electric signal becomes large, the superposed area between the fixed electrode layer 112 and the vibrating film 115 is preferably extended as possible as larger. Therefore, the fixed electrode layer 112 occupies a major area on the semiconductor substrate 111, and the elements to be integrated are arranged in the remaining area.
The capacitor microphone cannot be essentially housed in a completely sealed case. It must have a structure enabling air vibration to reach the vibrating film 115 through the hole 116. To maintain the state where the air vibration can be reached means incapability of completely interrupting light. In addition, the vibrating film is a film not having complete light-shielding characteristics and has a transmittivity of several %.
The circuit elements integrated on the semiconductor substrate 111 involve formation of some PN junctions. When light is incident to the silicon substrate having these PN junctions, a dark current is generated owing to optical electromotive force. The generated dark current flows into the circuit elements, thus leading to sound noise of the ECM and malfunction of the circuit.
The present invention has been accomplished in view of the problem as described above. An object of the invention is to provide a reliable circuit element capable of preventing malfunction due to a dark current.
In the first invention, the above object is achieved in such a manner that wherein an electronic circuit formed outside a fixed electrode layer is covered with a shield metal.
The second invention is characterized in that the shield metal is formed at the same potential as that at the vibrating film.
The third invention is characterized in that the shield metal is formed to extend from the upper surface of the electronic circuit to a side surface thereof.
The fourth invention is characterized in that the shield metal is in contact with a semiconductor region having one conduction type formed in the surface of the semiconductor substrate and connected to ground potential through the semiconductor substrate.
The fifth invention is characterized in that the the semiconductor device further comprises a shield wiring made of a conductor material formed so as to surround the electronic circuit substantially, an insulating film covering the shield wiring, and an opening in the insulating film which exposes a surface of the shield wiring, wherein the shield metal is electrically connected to the shield wiring through the opening.
The sixth invention is characterized in that the shield wiring is a conductive film filled in a through-hole formed in a second insulating film covering the surface of the semiconductor substrate, the shield wiring being formed in a line so as to surround at least an inside region of the electronic circuit.
The seventh invention is characterized in that the shield wiring is a conductive film filled in a through-hole formed in a second insulating film covering the surface of the semiconductor substrate, the shield wiring being formed in a line so as to surround at least an outside region of the electronic circuit.
The eighth invention is characterized in that the shield wiring is a conductive film filled in a through-hole formed in a second insulating film covering the surface of the semiconductor substrate, the shield wiring being formed in a line so as to surround at least an outside region of the electronic circuit.
The ninth invention is characterized in that the fixed electrode layer is arranged substantially centrally on the semiconductor substrate; the shield wiring is composed of an electrode wiring for connecting circuit elements of the electronic circuit to one another and a wiring layer on the same level as the electrode wiring so that it substantially surrounds the electronic circuit.
The tenth invention is characterized in that a surface of the shield wiring is covered with an insulating film, the shield wiring being electrically connected to the shield metal through the opening formed in the insulating film.
The eleventh invention is characterized in that it comprises a semiconductor substrate, a fixed electrode layer arranged substantially centrally on the semiconductor substrate, an electronic circuit located outside the fixed electrode layer, an electrode wiring for connecting circuit elements of the electronic circuit; a shield wiring on the same level as the layer where wirings constituting the electronic circuit and substantially encircling the electronic circuit; an insulating film in which the shield wiring is exposed; a shield metal which is connected to the shield wiring through an exposed area of the shield wiring and covers the electronic circuit; and a spacer for attaching a vibrating film which constitutes a capacitor in a pair with the fixed electrode layer.
The twelfth invention is characterized in that it further comprises: a pad electrode serving as an external electrode of the electronic circuit and the shield metal is partially removed above the pad electrode.
The thirteenth invention is characterized in that the shield metal is made of an Alxe2x80x94Si film.
The fourteenth invention is characterized in that the shield metal is connected to ground potential GND.
The fifteenth invention is characterized in that it comprises: a fixed electrode layer formed on a surface of a semiconductor substrate, an electronic circuit formed on the surface of the semiconductor substrate on the periphery of the fixed electrode layer, and a spacer for attaching a vibrating film which constitutes a capacitor in a pair with the fixed electrode layer, and in that a surface of the semiconductor substrate corresponding to a region where the electronic circuit is formed is covered with an insulating film and the electronic circuit is covered with a shield metal formed on the insulating film; and the same material as the shield metal is continuously extended to the surface of the semiconductor substrate so as to surround the region where the electronic circuit is formed.
For example, in the case of a two-layer metallic wiring, the shield wiring, a through-hole which exposes it and a shield metal can completely shield the electronic circuit.
The above and other objects and features of the invention will be more apparent from the following description taken in conjunction with the accompanying drawings.